It is important to understand why children make errors. A few studies, none of which employed children, suggest that the time between responses on conditional discriminations may be critical to error production. To expand this knowledge, the time allowed between children's discriminated responses will be manipulated on a conditional discrimination task, matching-to-sample. This task appears frequently in educational procedures and is currently being employed in psychodiagnostics. After gathering baselines of children's error performance and relative frequency distributions of the time between responses to the sample stimuli and subsequent match attempts (defining choice times or CRTs), reinforcement will be made contingent on the emission of a class of these CRTs different from the average produced during baseline. In a second experiment, CRTs produced by various schedules of reinforcement for matching will be measured and analyzed for their relationship with error production. The results will clarify the role of interresponse times in children's complex, discriminated operant behavior particularly with respect to the production of errors.